ABSTRACT Physical activity (PA), including regular exercise, prevents weight gain, delays functional limitations, and improves cardiovascular function, yet one in three Americans is inactive. PA measurement and promotion in underserved populations, such as low-income race/ethnic minority communities, is especially challenging. Inadequate cultural adaptation contributes to substantial measurement error between self-administered and continuously-monitored (e.g., device-based) PA assessments. Identification of the determinants of PA, within the context of sociocultural and geographic norms, is a central component of developing sustainable and cost- effective PA promotion strategies. Emerging evidence suggests that culturally-adapted PA promotion strategies, such as those that use community health workers, can provide cultural interpretation and adaptation of measurement and intervention, sensitivity to sociocultural norms, and increase treatment adherence and social support of intervention activities. However, these interventions are difficult to scale. Mobile health (mHealth) technology, including text messaging, has shown great promise for behavioral interventions and disease self- management, but common concerns include the impersonalized nature of texts and uncertainty regarding effective frequency and content. Culturally-adapted health coaching and social support provided by community health workers, combined with frequent contact via text messaging, may be an effective, scalable PA promotion tool, but the feasibility is not well understood among underserved communities. This career development award will provide me with training in health behavior theories, PA measurement strategies, and peer support and mHealth intervention development and evaluation. We propose to conduct an analysis of PA in the longitudinal Study of Women?s Health Across the Nation, a diverse sample of women that have been followed for 20 years, and recruit a sample of 60 Mexican-heritage Latina women from a federally-qualified health center to compare self-administered and device-based PA data among multiple race/ethnic groups (Aim 1). Then, we will develop (Aim 2) and pilot (Aim 3) a PA behavioral intervention using community health workers and mHealth tools to increase social support and PA among Latina participants. The goal of this Mentored Research Scientist Development Award (K01) is to prepare Dr. Kelly Ylitalo to become an independent investigator with expertise in innovative PA promotion throughout the lifecourse, with a specific emphasis on culturally-adapted measurement and intervention, to support the long-term goal of preventing or delaying functional limitations and aging-related disability in priority populations.